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https://github.com/LCPQ/quantum_package
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94 lines
3.2 KiB
Fortran
94 lines
3.2 KiB
Fortran
subroutine pt2_epstein_nesbet(det_pert,c_pert,e_2_pert,H_pert_diag,Nint,ndet,N_st)
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use bitmasks
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implicit none
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integer, intent(in) :: Nint,ndet,N_st
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integer(bit_kind), intent(in) :: det_pert(Nint,2)
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double precision , intent(out) :: c_pert(N_st),e_2_pert(N_st),H_pert_diag(N_st)
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double precision :: i_H_psi_array(N_st)
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BEGIN_DOC
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! compute the standard Epstein-Nesbet perturbative first order coefficient and second order energetic contribution
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!
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! for the various N_st states.
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!
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! c_pert(i) = <psi(i)|H|det_pert>/( E(i) - <det_pert|H|det_pert> )
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!
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! e_2_pert(i) = <psi(i)|H|det_pert>^2/( E(i) - <det_pert|H|det_pert> )
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!
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END_DOC
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integer :: i,j
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double precision :: diag_H_mat_elem, h
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PROVIDE selection_criterion
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ASSERT (Nint == N_int)
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ASSERT (Nint > 0)
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call i_H_psi(det_pert,psi_selectors,psi_selectors_coef,Nint,N_det_selectors,psi_selectors_size,N_st,i_H_psi_array)
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h = diag_H_mat_elem(det_pert,Nint)
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do i =1,N_st
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if(CI_electronic_energy(i)>h.and.CI_electronic_energy(i).ne.0.d0)then
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c_pert(i) = -1.d0
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e_2_pert(i) = selection_criterion*selection_criterion_factor*2.d0
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else if (dabs(CI_electronic_energy(i) - h) > 1.d-6) then
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c_pert(i) = i_H_psi_array(i) / (CI_electronic_energy(i) - h)
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H_pert_diag(i) = h*c_pert(i)*c_pert(i)
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e_2_pert(i) = c_pert(i) * i_H_psi_array(i)
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else
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c_pert(i) = -1.d0
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e_2_pert(i) = -dabs(i_H_psi_array(i))
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H_pert_diag(i) = h
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endif
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enddo
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end
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subroutine pt2_epstein_nesbet_2x2(det_pert,c_pert,e_2_pert,H_pert_diag,Nint,ndet,N_st)
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use bitmasks
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implicit none
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integer, intent(in) :: Nint,ndet,N_st
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integer(bit_kind), intent(in) :: det_pert(Nint,2)
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double precision , intent(out) :: c_pert(N_st),e_2_pert(N_st),H_pert_diag(N_st)
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double precision :: i_H_psi_array(N_st)
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BEGIN_DOC
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! compute the Epstein-Nesbet 2x2 diagonalization coefficient and energetic contribution
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!
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! for the various N_st states.
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!
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! e_2_pert(i) = 0.5 * (( <det_pert|H|det_pert> - E(i) ) - sqrt( ( <det_pert|H|det_pert> - E(i)) ^2 + 4 <psi(i)|H|det_pert>^2 )
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!
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! c_pert(i) = e_2_pert(i)/ <psi(i)|H|det_pert>
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!
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END_DOC
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integer :: i,j
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double precision :: diag_H_mat_elem,delta_e, h
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ASSERT (Nint == N_int)
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ASSERT (Nint > 0)
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PROVIDE CI_electronic_energy
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call i_H_psi(det_pert,psi_selectors,psi_selectors_coef,Nint,N_det_selectors,psi_selectors_size,N_st,i_H_psi_array)
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h = diag_H_mat_elem(det_pert,Nint)
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do i =1,N_st
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if (i_H_psi_array(i) /= 0.d0) then
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delta_e = h - CI_electronic_energy(i)
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if (delta_e > 0.d0) then
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e_2_pert(i) = 0.5d0 * (delta_e - dsqrt(delta_e * delta_e + 4.d0 * i_H_psi_array(i) * i_H_psi_array(i)))
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else
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e_2_pert(i) = 0.5d0 * (delta_e + dsqrt(delta_e * delta_e + 4.d0 * i_H_psi_array(i) * i_H_psi_array(i)))
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endif
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if (dabs(i_H_psi_array(i)) > 1.d-6) then
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c_pert(i) = e_2_pert(i)/i_H_psi_array(i)
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else
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c_pert(i) = 0.d0
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endif
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H_pert_diag(i) = h*c_pert(i)*c_pert(i)
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else
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e_2_pert(i) = 0.d0
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c_pert(i) = 0.d0
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H_pert_diag(i) = 0.d0
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endif
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enddo
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end
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